The present invention relates to packaging materials and in particular, to a sheet or foil construction from which packages, containers, bags or the like can be formed and to the packages, containers and bags made therefrom.
Plastic material has been used to form packages, containers, etc., for consumer items such as foods, medicines, hardware and other obvious products. As is well known, bags which are sealed in order to protect and keep their products free of contamination, are difficult to open. Various attempts have been made to provide such containers with tear means which are intended to facilitate opening. For obvious reasons such means are always located in the actual sealing weld by which the container is closed, since there would otherwise be considerable risk of leakage or permeability to air, if the tear strip, perforations, or other means were to be placed elsewhere. By placing the tear-means in the sealing weld, however, the container becomes difficult to open as the weld reinforces the strength of the container. The initial force required often is so great that container is destroyed and the contents spilled, or open to contamination. Furthermore, such means always entail the sealing of the material to both sides or walls of the container which requires the use of special mechanical equipment for the manufacture and filling of the container.
It has also been proposed to make a container, such as a bag, of several layers of sheet material having front and rear sides of a thermoplastic material or one which could be heat-welded, with a tear strip of said material welded together with all the sheets forming the bag at the point where the bag should be opened. The bag material, as well as the strip for welding to the bag material, in this case would consist entirely of material which can be heat-sealed, i.e. polyethelene, polypropylene, polyvinyl chloride, cellulose fibres or the like, and the strip is welded to the bag by means of an external weld through all the layers. It has been found that this method of welding on the tear-off strip does not give a satisfactory solution of the problem since, in order to achieve the required seal between all the layers of material, a relatively strong outer weld must be applied, which in turn causes difficulty in opening and an uncontrolled tear. Relatively great initial force must be used with this tear strip and it is thus very easy to acquire a tear which follows an arbitrary and poorly defined path.
It is an object of the present invention to provide a foil or sheet for use in packaging material which provides improved means for tearing the same.
It is an object to provide a foil or sheet which is provided with a reinforced seam of its own material which may be used as the tear strip.
It is also an object of the present invention to provide improved means and method for forming foils with an integral tear strip.
These objects, others and numerous advantages will be set forth and apparent from the following description of the invention.